Scientists have discovered that brief patterns of brain activity usually seen during deep sleep frequently intrude into the waking hours of adults with attention deficit hyperactivity disorder. This phenomenon tends to explain why individuals with the condition experience frequent lapses in attention and excessive daytime sleepiness. The findings, published in The Journal of Neuroscience, provide evidence that attention deficit hyperactivity disorder might be deeply connected to how the brain regulates the boundary between sleep and wakefulness.
Adults with attention deficit hyperactivity disorder frequently face challenges with sustained focus, behavioral variability, and impulsivity. They also tend to report higher rates of sleep disturbances and daytime tiredness than the general population. This combination of symptoms led researchers to wonder if there might be a physical overlap between sleep and attention systems in the brain.
“My interest grew out of our earlier work which looked at how medications like methylphenidate (MPH; commonly known as Ritalin) affect slow waves during wakefulness in neurotypical individuals,” explained Elaine Pinggal, a research fellow at Monash University. “What intrigued me was how MPH is typically used to treat both narcolepsy and ADHD, conditions that are quite different on the surface.”
When their findings showed that this medication reduced these slow wave occurrences, it raised the question of whether slow waves during wakefulness might play a meaningful role in the condition. Thomas Andrillon, a researcher at the Paris Brain Institute and senior author of the study, recognized the potential of this idea. “It was really Thomas who first had the vision to bring this question into a clinical ADHD population, and it’s been a privilege to be a part of this work,” Pinggal said.
To investigate this, scientists recruited 63 young adults with an average age of 23. The sample included 32 adults formally diagnosed with attention deficit hyperactivity disorder and 31 neurotypical adults without the condition. The participants with the disorder were asked to stop taking their standard medications for 72 hours before the experiment to ensure their brain activity was measured in an unmedicated state.
During the experiment, participants completed a computer-based task designed to test sustained attention over a 52-minute period. Numbers from one to nine flashed on a screen in continuous sequences. Participants were instructed to press a button as quickly as possible for every number except the number three. This repetitive activity required constant vigilance and the ability to hold back impulsive reactions.
While participants completed the task, the researchers continuously recorded their brain activity using an electroencephalogram. This involved placing a cap with 64 specialized sensors on the scalp to measure electrical signals in the brain. The scientists specifically looked for high-amplitude slow waves that indicate localized parts of the brain are temporarily slowing down and entering a sleep-like state.
“The intrusion of sleep waves is a perfectly normal phenomenon. Think of a long-distance run: after a while, physical fatigue forces you to take a break. The same applies to mental fatigue,” Andrillon explained. “After a day spent awake or following a poor night’s sleep, the brain also takes breaks in the form of slow waves.”
Pinggal agreed, noting that the brain briefly goes offline for local recovery. “The first thing I’d want people to know is that these sleep-like slow waves during wakefulness aren’t unique to people with ADHD; they happen to everyone,” Pinggal told PsyPost. “They’re more likely to occur the more tired you are, or the longer you’ve been doing a task.”
However, the study found a difference in the frequency of these events. “These brief moments of reduced brain activity occur in everyone. In people with ADHD, however, this activity is more frequent,” Andrillon added. “Our results suggest that it could be a key brain mechanism explaining their difficulties in maintaining stable attention and performance over time.”
Every 40 to 70 seconds, the computer task paused to ask participants what they were thinking about just before the interruption. They could report being actively on task, mind wandering, experiencing mind blanking, or not remembering. Mind wandering involves thinking about personal matters or distractions unrelated to the task. Mind blanking refers to moments where the mind is completely empty of conscious thought.
The behavioral results showed distinct performance differences between the two groups. Adults with attention deficit hyperactivity disorder made significantly more commission errors, meaning they frequently pressed the button when they were supposed to hold back. Their reaction times were also much more variable from one moment to the next compared to the neurotypical group, reflecting fluctuating levels of attention.
“A few things stood out. One was around mind wandering: in neurotypical participants, mind wandering was reported as being more intentional, like a deliberate mental break,” Pinggal noted. “However, in participants with ADHD, they reported more unintentional mind wandering i.e., it just happened without them choosing for their attention to drift.”
Pinggal also highlighted an unexpected result regarding fatigue. “Another surprising finding was around sleepiness: a natural assumption might be that if you have ADHD and struggle with sleep, you’d feel more tired throughout the day,” Pinggal said.
“However, in our cohort we actually found that there wasn’t a difference in daytime sleepiness between the two groups,” she continued. “What differed was that participants with ADHD felt sleepier during the task itself, suggesting that their brains may fatigue more quickly under sustained effort, rather than being generally sleepier people. That said, this was one cohort; more research is definitely needed before drawing broader conclusions.”
The brain activity recordings provided evidence that explains these behavioral differences. “Adults with ADHD show a significantly higher density of slow waves, which are usually observed during deep sleep,” Andrillon said. “These waves are not trivial: the higher their density, the more participants make inattentive errors and show slower or more variable reaction times.”
To understand the relationship between the medical diagnosis, brain activity, and performance, the researchers used a statistical tool called mediation analysis. This technique tests whether a middle variable explains the link between a starting factor and an outcome. The analysis suggests that the increased presence of waking slow waves is a primary physical mechanism driving the attentional difficulties seen in the condition.
Because of this strong association, tracking these brain patterns could offer clinical utility. “These local sleep waves could become a key biomarker for diagnosis,” Andrillon said.
While the study provides a detailed neurophysiological explanation for attention difficulties, the scientists acknowledge some limitations. “Before any of this could responsibly inform real-world treatment, we’d need replication of these findings, larger and more diverse cohorts, longer-term studies, and a much clearer picture of the underlying mechanisms,” Pinggal explained.
“We also can’t yet say which comes first: does ADHD make sleep harder, or does poor sleep drive ADHD symptoms?” Pinggal cautioned. “These two probably feed into each other, but unpicking the causal direction requires longitudinal research. Our findings point to slow waves during wakefulness as a potential contributor to attentional difficulties, though how this relates to sleep more broadly remains to be established.”
“One exciting next step for this line of research is the use of auditory stimulation during sleep,” Pinggal added. “This involves playing quiet tones timed to the upswing of slow waves during sleep to boost slow wave activity. This approach has shown promising results in boosting slow wave activity in those who respond to it, and has been shown to improve memory and cognition.”
“The mechanism isn’t fully understood yet, but the idea is that by strengthening slow waves during sleep, the brain may have less need to produce them during wakefulness,” Pinggal concluded. “It’s likely just one piece of a larger puzzle, but it’s a promising avenue, and one where our research on slow waves during wake could help clarify the broader picture.”
The study, “Sleep-Like Slow Waves during Wakefulness Mediate Attention and Vigilance Difficulties in Adult Attention-Deficit/Hyperactivity Disorder,” was authored by Elaine Pinggal, James Jackson, Anikó Kusztor, David Chapman, Jennifer Windt, Sean P. A. Drummond, Tim J. Silk, Mark A. Bellgrove, and Thomas Andrillon.
